The enclosing or encasing of cylindrical objects during the course of the extrusion of a plastic sleeve has long been known. e.g. in the production of covered cables or the like. Furthermore it is known to introduce discrete cylindrical objects into a tube during the course of the extrusion thereof. Thus, for example, in U.S. Pat. specification Ser. No. 2,484,965 (Slaughter) there is disclosed a method of making extruded collapsible tubes which essentially consists of extruding a continuous tube by means of an extrusion cross head and successively feeding into the extrusion successive spaced-apart tube closures so that the tube is formed around the closures.
Similarly, in U.S. Pat. specification Ser. No. 2,575,138 (Slaughter) there is disclosed a process for packaging cylindrical articles within a continuous tube comprising the steps of extruding the tube by means of an extrusion cross head, successively feeding the articles to be packaged through the cross head so as to be enclosed by the tube, the portions of the tube between the successive enclosed articles being subsequently sealed and severed.
In both cases the tube is extruded by an angular extrusion nozzle (known as an extrusion cross head) with the cylindrical objects being successively fed into the cross head by means of an appropriate pusher mechanism.
In completely analogous fashion there is disclosed in U.S. Pat. Specification No. 3,981,452 the application of this known process in the production of an irrigation conduit in which are located at predetermined intervals, successive cylindrical units which together with the inner surface of the conduit form a plurality of emitter units.
In all cases of the prior art referred to above, the element to be enclosed by the extruded tube, whatever its nature, is of cylindrical shape and is wholly enclosed by the extruded tube.
The present invention, on the other hand, relates particularly to the production of a drip irrigation conduit, wherein the internally bonded emitter units are not of circular cross section extending across the entire periphery of the surrounding conduit, but are of limited depth with the bonded area thereof extending into the conduit for less than half the diameter thereof. Drip irrigation conduits having emitters of this kind are, for example, disclosed in our earlier U.S. Pat. No. 4,307,841.